1. Field of the Invention
The invention relates to a liquid crystal display device having high response speed and a method for driving the same using applied voltage waveform for achieving high response speed.
2. Description of the Related Art
An active matrix driving method has conventionally been used for conducting multiple gray-scale display using a liquid crystal display device. The active matrix driving method is a method in which a reference voltage corresponding to a display gray-scale is selected with an analog switch, and the selected voltage is applied to a liquid crystal display device to display a desired display gray-scale. One gray-scale is generally displayed in a period in which an image is displayed (one frame), and a predetermined reference voltage corresponding to the desired gray-scale is applied to the liquid crystal display device.
When change in the voltage applied to the liquid crystal display device is small, the time within which the desired gray-scale is obtained (response time, namely, rise time plus fall time) tends to increase. Increase in response time cause a problem of blur since the response of a liquid crystal is late when the change in voltage applied to the liquid crystal display device, for example, change from a halftone 1 to a halftone 2 is small. Correspondingly, for example, comparing the gray-scale data for the previous time and the next time, the voltage to be applied is increased when the gray-scale data for the previous time is more, and is reduced when the gray-scale data for the present time is less, conventionally. Thus, the rise time is reduced by overdriving, for example, by making the voltage actually applied or a part thereof higher or lower than the reference voltage corresponding to the desired gray-scale, thereby solving the problem.
In the case of conducting such overdriving, the scale of circuit becomes larger, which causes a fear of high cost. Correspondingly, a driving method with which response speed of gray-scale change of a liquid crystal display panel can be improved using small memory capacitance has been proposed (Reference 1: Japanese Patent Laid-Open No. 07-121143).
However, in the case of conducting such overdriving with a liquid crystal display device, the circuit for comparing the previous and present gray-scale data, the circuit for converting the gray-scale data upon the comparison result, and the like complicate the structure of the liquid crystal display device.
Further, since hold driving by which the voltage applied is kept throughout one frame period is conducted in a liquid crystal display device, it is not sufficient to decrease the rise time due to high applied voltage for a countermeasure against blur of moving images.